Magnetic after-effect measurements of thermally aged and neutron irradiated, cold-worked Fe-Cu model alloys are performed in the temperature range between 100 K and 500 K in order to study the effects of copper precipitates and the irradiation induced defects on dislocation relaxation processes. For these two conditions, by increasing the level of plastic deformation, we show the clear difference in the behavior of dislocation related peaks. The effect of irradiation induced defects on dislocations is clearly pronounced by the increased number of relaxed dislocations compared to the number in the thermally aged samples. Furthermore, we observe a non-monotonic change in the behavior of the intensities of dislocation-related peaks in neutron irradiated samples, which occurs due to dislocation annihilation of the irradiation induced defects.